Mix together ripe/active sourdough starter with all-purpose or bread flour and water. Cover loosely and let sit 10-12 hours at 78-80°F until doubled, bubbly & peaked.Note: If you have a ripe, bubbly, active sourdough starter that is fed equal parts flour and water – it can be substituted equally for the levain in this recipe.

Mix Dough: To a large bowl, mix together ripe levain with water. Add salt and bread flour. Mix together using a dough whisk or spoon until a wet and sticky dough forms and the ingredients are fully combined. Cover and let rest for 30 minutes.Note: This dough is very sensitive to temperature. It's important to maintain a temperature where the dough will rise AND the butter stays chilled and flaky. I've found a 70-72ºF temperature to work well. I wouldn't go above 75ºF for this recipe or the butter will get too soft. To do this, use cooler water when mixing your dough and take the temperature with a thermometer throughout the process.

Stretch and Folds: After the dough has rested, you will perform a series of “stretch and folds” over the next 1 ½ hours. The goal is to strengthen the dough through a gentle kneading process. You will also add cold butter into the dough during this process which will be evenly dispersed throughout the dough through the folds. To “stretch and fold,” wet your hand (so it doesn’t stick to the dough). Reach around the dough down to the bottom of the bowl, pull the dough up and over and place it on top of the dough. Turn the bowl a quarter turn and repeat the stretch and fold. Turn another quarter turn and repeat. Perform one more quarter turn, stretching and folding the dough. Cover and set aside. Take note of how the dough feels through this process. It will go from feeling a little shaggy to smooth and elastic. Cover the bowl and wait about 30 minutes in between stretch and folds.

Stretch and fold #1: After 30 minutes, perform your first set of stretch and folds. Cover the dough and let rest for 30 minutes.Stretch and fold #2: After 30 minutes, grate the cold (or frozen) butter. Put half of the grated butter on top of the dough. The other half of the butter should be placed in the refrigerator to chill until the next set of folds. Stretch and fold the dough again, incorporating the flakes of butter into the dough. Cover and let rest for 30 minutes.Stretch and fold #3: 30 minutes later, add the rest of the butter to the top of the dough. Stretch and fold again. The butter will continue dispersing throughout the dough. Cover and let rest for 30 minutes.Stretch and fold #4: After 30 minutes do your final set of stretch and folds. You should notice the dough feeling more cohesive and strong. If your dough still feels loose, add in another couple stretch and folds to help strengthen and tighten the gluten strands.Note: If you find the butter is difficult to grate, freeze it and grate the butter frozen. You may need to add a little extra time ot the rest/bulk fermentation to compensate for a colder dough.

Rest/Bulk Fermentation: Cover the dough and let rise for 6-7 more hours. You will know the dough is ready to shape when the dough has risen about 70%, jiggles when you shake the bowl and has scattered bubbles visible on the sides and top.

Prepare 2 baking sheets and line them with parchment paper.

Shape: Dump the dough out on the counter and use your hands to gently lift and pull it into a 12 by 24-inch rectangle. The dough should not rip during this if you work gently. If it does, just patch it up. Use a bench scraper to portion the dough into 12 pieces. Cut the dough into six 4 by 12-inch slices. Then cut those slices in half, giving you twelve 4 by 6-inch rolls.Take a chocolate baton (or slice of chocolate bar or chocolate chips) and place one at the bottom end of each rectangle of dough. Place the other piece of chocolate at the top of the rectangle. Roll the dough up once from the bottom and once from the top down - they will meet in the middle. Place the croissant roll on a parchment-lined baking sheet, about 6 croissant rolls on each baking sheet.

Proof: Cover the pan of dough with plastic wrap or a baking sheet cover and proof for 2-3 hours until puffed up and jiggly. During this final proofing, I like to warm the dough up to 75ºF using a dough warming mat, or setting the dough on top of a warm appliance.Once the rolls have puffed up and almost doubled in size, you can either bake them right away or stick them in the refrigerator overnight to bake straight from the fridge in the morning.

Bake: Preheat the oven to 425ºF. Whisk together a simple egg wash by adding an egg with a splash of water to a small bowl and whisking together. Brush egg wash on top of croissant rolls. Bake rolls for 10 minutes at 425ºF. After 10 minutes, rotate the pan and reduce the temperature to 350ºF. Bake for another 20 minutes until golden brown.

Remove the croissant rolls to a cooling rack and let cool for 10-20 minutes before enjoying!